An ATV typically includes three or four wheels disposed one behind the other along each side of the vehicle, the axles of which usually are all constrained to move in unison by means of gears and chains. The vehicle is skid-steered.
Typically, an ATV has no suspension in the normal sense. The tires are extremely elastic and provide all the suspension resilience that is needed.
The tires are set to a very low pressure, typically in the region of one sixth of atmospheric pressure. Such tires are very flexible, and the bulge of the tire, where the weight of the ATV rests on it, is very marked. The difference in width between a bulged and an unbulged tire profile can be around 4 cm.
An ATV has an extremely powerful drive capability over most off-road surfaces. Even so, the ATV user sometimes finds it desirable to fit tracks over the wheels to improve the traction when travelling over such surfaces, for example, as wet snow upon hard ice, or just-thawing mud.
Optional add-on tracks are therefore offered by ATV manufacturers for fitting over the tires.
If such a track is allowed to wander sideways with respect to the tires, then it soon happens that the very flexible tires start to climb over the segments of the track, and the track is shed. Experience has shown that if the track has a permitted slack on the wheel of more than a millimetre or two, measured laterally of the track, the track will not stay on.
It has been proposed to locate the segments from the sides of the laden, bulged profile of the tires. The segment is inevitably therefore well clear of the unbulged profile. This is not satisfactory.
In this case, the track being in contact with half the circumference each of the front and back wheels of the ATV, the track is not located laterally until it is right under these wheels.
Those parts of the track not actually under the wheels are in engagement with the unbulged, unloaded profile of the wheel, and are not adequately located laterally. The result is that the tires climb out of the tracks.
To cure the track-shedding problem, manufacturers have found it necessary hitherto to locate the tires from the unbulged profile. This is effective to retain the track on the ATV, but it carries the great disadvantage that the bulge of the tire now has to squeeze through the segments of the track, since the track is adapted to engage the unbulged profile of the tire.
So much engine-power is required to squeeze the tires through the segments that the top-speed of the ATV is reduced, typically, by as much as 50%. And also, the constant manipulation of the loaded part of the tire can lead to early tire failure.